A number of substituted imidazo[4,5-b]quinolin-2-ones are known from BE-904,671; DE-A-3,717,291; U.S. Pat. Nos. 4,710,459 and 4,943,573 as phosphodiesterase and blood platelet aggregation inhibitors which are useful as isotropic cardiotonics and antithrombotics.
In U.S. Pat. No. 5,043,327 which corresponds to EP-A-0,406,958, published Jan. 9, 1991, there are described positive isotropic and lusitropic 3,5-dihydro-imidazo[2,1-b]quinazolin-2(1H)-one derivatives.